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logging

Logging​

log — Leveled Logging​

LEVEL-DEBUG = 0
LEVEL-INFO  = 1
LEVEL-WARN  = 2
LEVEL-ERROR = 3
LEVEL-FATAL = 4

log.set-level(lvl)                     // Set the minimum log level
log.debug(msg)
log.info(msg)
log.warn(msg)
log.error(msg)
log.fatal(msg, code)                   // Log and exit with the given status code

Output format​

Combine format bits with set-format (default is F-LEVEL only, close to the legacy output):

F-TIME  = 1                            // Timestamp YYYY-MM-DD HH:MM:SS (UTC)
F-LEVEL = 2                            // [INFO] / [ERROR] level tag
F-LOC   = 4                            // Call site [file:line:col]

log.set-format(log.F-TIME | log.F-LEVEL | log.F-LOC)
log.info('server started')             // 2026-.. ..:.. [INFO] app.no:7:5 server started

The F-LOC "file:line:col" is injected automatically by the compiler at the call site via #{track-caller} — no manual argument needed. Each of debug / info / warn / error / fatal has a trailing optional loc str = '' slot (when passed explicitly the given value wins, so wrappers can forward their own location).

Output target (stderr / file)​

Logs go to standard error (fd=2) by default. Switch to a file or any io.writer:

log.open-file(path)                    // Open file in append mode and set as target; returns ?bool
log.set-output-fd(fd)                  // Switch to a custom fd (caller opens/closes it)
log.set-writer(w io.writer)            // Switch to an io.writer (uses its fd)
cur = log.get-output-fd()              // Current output-target fd
w = log.get-writer()                    // Current output target as an io.writer
log.set-format(log.F-TIME | log.F-LEVEL | log.F-LOC)
log.open-file('app.log')               // Subsequent lines append to app.log
log.error('disk full')                 // [ERROR] [main.no:12:5] disk full → app.log